Synthesis of 4-substituted phenyl (11H,16H-5,6-dioxa-11a,15b-diaza-5aλ 5 -phosphabenzo[b] naphtha-[2, 3-l] fluoren-5-yl) ether (4a-j) were accomplished via two step process. It involves the prior preparation of monochloride intermediate (2) and its subsequent reaction with various phenols in dry tetrahydrofuran in the presence of TEA under reflux condition. These compounds were characterized by IR, 1H, 13C and 31P NMR and were found to exhibit potent antimicrobial activity.